Tcl_GetOpenFile(3)

💖 Tcl_GetOpenFile — bestie edition 💖

okay so this is a page from the Tcl Library Procedures manual, and today we're talking about Tcl_GetOpenFile. it's giving "let me hand you the actual FILE* bestie" energy ✨

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✨ NAME ✨

Tcl_GetOpenFile — Return a FILE* for a channel registered in the given interpreter (Unix only) 🦋

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🌸 SYNOPSIS 🌸

#include <tcl.h>

int
Tcl_GetOpenFile(interp, chanID, write, checkUsage, filePtr)

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🎀 ARGUMENTS 🎀

• Tcl_Interp *interp (in) — the Tcl interpreter you're grabbing the file handle from.
• const char *chanID (in) — a string that names the channel, like stdin or file4, iykyk.
• int write (in) — non-zero means this file is gonna be used for writing, zero means it's for reading.
• int checkUsage (in) — if it's non-zero, an error gets generated when the file was not opened for the access that write says it's for. rude of it to check, but okay.
• void **filePtr (out) — points to the word where we're gonna stash the pointer to the FILE structure for the file that chanID names. 💅

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👑 DESCRIPTION 👑

so Tcl_GetOpenFile takes, as its argument, a file identifier of the form returned by the open command, and it returns at *filePtr a pointer to the FILE structure for that file. iconic.

the write argument tells it whether that FILE pointer is gonna be used for reading or writing. and here's the tea: in some cases — like a channel that connects to a pipeline of subprocesses — you get different FILE pointers back for reading versus writing. not me getting two different doors for the same room 😭

Tcl_GetOpenFile normally returns TCL_OK. but if something goes wrong — like chanID didn't make any sense, or checkUsage was set and the file wasn't opened for the access that write specified — then TCL_ERROR comes back and the interpreter's result will hold an error message. 💀

fr fr heads up: in the current implementation, checkUsage is ignored and consistency checks are always performed. so that flag is lowkey just vibing there.

also, important: this interface is only supported on the Unix platform. periodt. 🐧

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🔥 KEYWORDS 🔥

channel, file handle, permissions, pipeline, read, write

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and that's the whole page bestie, no cap, every flag and caveat intact 🫶

this one came from the Tcl manual, version 8.0, and the page is Tcl_GetOpenFile(3) — go forth and slay your channels 💅✨